The present invention relates to improvements in air knife coaters for paper machines.
In an air knife coater for coating a traveling web of paper, the web is trained over a backup roll and coating is applied to the other surface of the web by various means such as by a coating roll. The air knife directs a thin high velocity sheet of air against the freshly applied coating on the web to either smooth the coating, and in some instances to both smooth the coating and doctor off excess coating. In coating, it is very important that the gap between the lips of the air knife orifice be accurately spaced from each other so that the flow of air forming the air knife be uniformly applied across the width of the machine. Since the gap is normally quite narrow (i.e., about 0.030"), it is important that the lips be firmly supported and be maintained clean.
For cleaning operation, the air knife assembly can be moved away from its operating position, but it has been found to be highly advantageous if the lips can be separated for cleaning the distal edge of each of the lips and for access to the slot between the lips. Such separation for cleaning must be followed by the lips again being moved back together to an accurate position so that the gap is once again accurately defined and maintained uniform across the machine.
In addition to being able to separate the lips for cleaning purposes, it is helpful to be able to separate the lips to have access to their inner surfaces for inspection. Experience in operation proves that conventional cleaning methods such as inserting a blade type object between the lips does not always clean the surfaces. With this type of cleaning, there is no way to totally inspect the surfaces to make sure foreign material is dislodged. Thus, if a cleaning operation is accomplished by the use of a blade type cleaner, and the air knife head is again put into operation, foreign material which is not removed but merely dislodged may affect the gap and the operator does not know this until operation is again begun, and the defect is detected by defects in the surface of the coat of paper.
It is accordingly an object of the present invention to provide an improved air knife coater which makes it possible to thoroughly clean the distal edges of the lips and the surfaces between the lips which form the gap in such a manner that cleanliness is assured, and the operator does not have to restart the machine to see if foreign materials have been fully dislodged and cleaned.
It is another object of the invention to provide an improved air knife coater wherein the lips can be separated quickly for inspection, and also for cleaning and wherein the lips can be quickly again closed to their predetermined accurate gap for returning them to operation.
A feature of the invention is to pivotally support one of the lips relative to the other, preferably the upper lip, and the pivotal support is constructed so as to supply rigidity to the upper lip maintaining it in proper relationship to the lower lip. In a preferred arrangement, the upper lip is divided into two parts with the lower portion narrowing down to an orifice in the usual manner. The lower portion is supported from the upper section with cams and locking screws so that the tip of the lip can be adjusted relative to the other lip in the usual manner. The upper portion of the lip is fitted with a rod the full width of the machine and held in place by clamps to form a hinge. The hinged lip is opened or held in operating position by toggle clamps which are adjustable.